DE 30 27 091 A1 discloses peripheral sealing means on a pressure cooker, in which case a pot and lid can be fastened together so as to be pressure-tight by means of peripheral segments formed along the lines of a bayonet lock with interposition, between the edge of the pot and the edge of the lid, of a sealing ring made of rubber elastic material, a circumferential, essentially cylinder-jacket-like peripheral section being bent downwards from the body of the lid and adjoined by the radially inward-curved peripheral segments of the lid. The outward-oriented rear part or spine of the sealing ring rests against the inside surfaces of the lid, and its inward-oriented sealing lips respectively rests against the inside surface of the pot and the inside surface of the body of the lid, in which case, in addition, the preferably symmetrical spine of the sealing ring has a circular cross-section over an angle of more than 90° in its upper half of largest circumference, and only rests against the body of the lid in a corresponding region of circular cross-section on the inside surface of a curved transitional portion of the body of the lid. The objective of providing a pressure cooker of the aforementioned type with an additional, i.e. possibly third, pressure safety device in addition to safety and venting valve means (DE-PS 1 247 581) and an overpressure valve device (DE-PS 976 952) is thus achieved by simple means. In this case, when a critical or limiting pressure is exceeded, a rotation and deflection of the sealing ring can occur in such a way as to form an opening.
CH 571 335 discloses a pressure cooker with a lid with a cylindrical edge which is detachably fixed onto the cooking pot by means of a bayonet lock and in which a sealing ring is inserted which has a sealing lip resting against the lid and against the edge of the cooking pot respectively and which covers at least one opening provided at the edge of the lid between two adjacent lugs of the bayonet lock, in which case in the section of the sealing ring covering the opening there is a weakened point reducing the cross-section of said sealing ring and the sealing lip resting against the edge of the pot has an indentation at its edge in the region of this weakened point. Thus a pressure cooker with an overpressure safety device formed by the sealing ring is said to be provided, with the overpressure safety device responding reliably and steadily without the need for the edge of the lid to be excessively weakened. However, the cylindrical downward-oriented peripheral portion of the lid openings are provided in the vicinity of recesses provided in the annular portion of the sealing ring which reduce the cross-section of said annular portion so that a weakened point is produced. In the region of said recesses, an indentation is provided at the edge of the sealing lip facing the edge of the cooking pot. In use, the sealing ring hermetically seals the interior of the cooking pot. If for particular reasons the pressure inside the pressure cooker rises, then when it reaches a specific overpressure the portion of the sealing ring lying in the region of the opening and having the recess is forced outwards through said opening. Thus the sealing lip associated with the edge of the cooking pot is moved outwards over the edge of the cooking pot until a portion of it no longer rests against the edge of the pot and the indentation establishes a connection between the interior of the pot and the atmosphere, through which steam starts to escape. This design is disadvantageous since openings must be provided in the edge of the lid, involving additional labour costs in terms of manufacture and resulting in a weakening of the edge of the lid. Moreover, the sealing ring must be made of relatively soft material so that it can achieve the necessary displacement and deformation in the portion designed for the release of pressure.
EP 0 684 001 B1 discloses a device for automatically controlling the pressure in pressure vessels by means of a seal which is inserted between the pot of the vessel and the lid and which has at least one circumferential portion with a recess on the outside and a reduced cross-section so that the circumferential portion of the seal is deformed by internal pressure produced when the vessel is in use and a predetermined value is exceeded. The deformation results in an escape and release of pressure from the vessel and the cross-section of the seal being reduced by the provision of the recess on its outside in conjunction with at least one notch on the inside. Here too, a deformation of the entire sealing ring is required in the portion designed for the release of pressure if the apparatus is to be functional.
CH 407 459 discloses a pressure cooker having a lid with cylindrical edge which is secured to the edge of the body of the pot by means of a bayonet lock and also holds a sealing ring on the edge of the pot. The sealing ring forms part of an overpressure safety device and is inserted in the lid. Provided in the cylindrical edge of the lid is an inlet or recessed area which is normally bridged by the sealing ring and into which the portion of the sealing ring bridging said recessed area is pressed in the event of an overpressure occurring in the hermetically sealed cooking pot. The pot body and the lid are provided with supporting means at the point corresponding to the recessed area provided in the edge of the lid for the sealing ring, so as to prevent downward compression of the sealing ring in the event of an undesirable steam overpressure in the hermetically sealed cooking pot and to thus prevent a dangerous discharge of steam. In this case, it is also disadvantageous that protuberances have to be provided on the outer cylindrical edge of the lid, with the aforementioned disadvantages. Similar pressure-release mechanisms are disclosed in U.S. Pat. No. 2,600,703 and U.S. Pat. No. 2,600,714.
CH 404 908 discloses a pressure cooker consisting of pot and lid, the edge of the pot and the edge of the lid having cams which together form a bayonet catch which, by turning the lid in one direction, can be brought into the locked position. The lid is provided with a sealing ring for hermetically sealing the interior of the pot, and additionally, between the cams, the edge of the pot has at least one indented area extending in the horizontal portion of the edge for the purpose, when the sealing ring is specifically deformed outwards in radial direction as a result of a dangerous overpressure inside the pot, of opening the connection between the interior of the pot and the pot's surroundings so that the internal pressure is lowered. This design calls for a specific disadvantageous configuration of the edge of the pot and, for functioning of the overpressure safety device, the sealing ring must twist on the inside surface relative to the edge of the pot so that an opening is actually produced for the release of pressure. A device of this type is unreliable and difficult to reproduce.
GB 2 208 131 A discloses a safety venting device for pressure cookers, in which a sealing ring seals the lid relative to the base of a cooking pot and also covers an opening in the lid or base which extends in an area just in front of the inside edge of the sealing ring. In the cylindrical portion of the edge of the lid, a slot is provided, through which, when a predetermined safe pressure is exceeded, the sealing ring can bulge out, resulting in the opening being uncovered for the venting of pressure. It is a disadvantage that this pressure-release mechanism also requires a number of openings to be provided in the vicinity of the edge of the lid. A similar pressure-release device is known from U.S. Pat. No. 4,276,990.